The present invention is concerned with novel biaryloxymethylarenecarboxylic acids and their pharmaceutically acceptable salts, their manufacture and their use as medicaments. The present invention further relates to pharmaceutical compositions containing these compounds.
Diabetes mellitus is a common and serious disorder, affecting 10 million people in the U.S. [Harris, M. I. Diabetes Care 1998 21 (3S) Supplement, 11C], putting them at increased risk of stroke, heart disease, kidney damage, blindness, and amputation. Diabetes is characterized by decreased insulin secretion and/or an impaired ability of peripheral tissues to respond to insulin, resulting in increased plasma glucose levels. The incidence of diabetes is increasing, and the increase has been associated with increasing obesity and a sedentary life. There are two forms of diabetes: insulin-dependent and non-insulin-dependent, with the great majority of diabetics suffering from the non-insulin-dependent form of the disease, known as type 2 diabetes or non-insulin-dependent diabetes mellitus (NIDDM). Because of the serious consequences, there is an urgent need to control diabetes.
Treatment of NIDDM generally starts with weight loss, a healthy diet and an exercise program. However, these factors are often unable to control the disease, and there are a number of drug treatments available, including insulin, metformin, sulfonylureas, acarbose, and thiazolidinediones. Each of these treatments has disadvantages and there is an ongoing need for new drugs to treat diabetes.
Metformin is an effective agent that reduces fasting plasma glucose levels and enhances the insulin sensitivity of peripheral tissue, mainly through an increase in glycogen synthesis [De Fronzo, R. A. Drugs 1999, 58 Suppl. 1, 29]. Metformin also leads to reductions in the levels of LDL cholesterol and triglycerides [Inzucchi, S. E. JAMA 2002, 287, 360]. However, it loses its effectiveness over a period of years [Turner, R. C. et al. JAMA 1999, 281, 2005].
Thiazolidinediones are activators of the nuclear receptor peroxisome-proliferator activated receptor-gamma. They are effective in reducing blood glucose levels, and their efficacy has been attributed primarily to decreasing insulin resistance in skeletal muscle [Tadayyon, M. and Smith, S. A. Expert Opin. Investig. Drugs 2003, 12, 307]. One disadvantage associated with the use of thiazolidinediones is weight gain.
Sulfonylureas bind to the sulfonylurea receptor on pancreatic beta cells, stimulate insulin secretion, and consequently reduce blood glucose levels. Weight gain is also associated with the use of sulfonylureas [Inzucchi, S. E. JAMA 2002, 287, 360] and, like metformin, they lose efficacy over time [Turner, R. C. et al. JAMA 1999, 281, 2005]. A further problem often encountered in patients treated with sulfonylureas is hypoglycemia [Salas, M. and Caro, J. J. Adv. Drug React. Tox. Rev. 2002, 21, 205-217].
Acarbose is an inhibitor of the enzyme alpha-glucosidase which breaks down disaccharides and complex carbohydrates in the intestine. It has lower efficacy than metformin or the sulfonylureas, and it causes intestinal discomfort and diarrhea which often lead to the discontinuation of its use [Inzucchi, S. E. JAMA 2002, 287, 360].
Because none of these treatments is effective over the long term without serious side effects, there is a need for new drugs for the treatment of type 2 diabetes.
In skeletal muscle and liver, there are two major pathways of glucose utilization: glycolysis, or oxidative metabolism, where glucose is oxidized to pyruvate; and glycogenesis, or glucose storage, where glucose is stored in the polymeric form glycogen. The key step in the synthesis of glycogen is the addition of the glucose derivative UDP-glucose to the growing glycogen chain, and this step is catalyzed by the enzyme glycogen synthase [Cid, E. et al. J. Biol. Chem. 2000, 275, 33614]. There are two isoforms of glycogen synthase, found in liver [Bai, G. et al. J. Biol. Chem. 1990, 265, 7843] and in other peripheral tissues including muscle [Browner, M. F. et al. Proc. Nat. Acad. Sci. U.S.A. 1989, 86, 1443]. There is clinical and genetic evidence implicating glycogen synthase in type 2 diabetes. Both basal and insulin-stimulated glycogen synthase activity in muscle cells from diabetic subjects were significantly lower than in cells from lean non-diabetic subjects [Henry, R. R. et al. J. Clin. Invest. 1996, 98, 1231-1236; Nikoulina, S. E. et al. J. Clin. Enocrinol. Metab. 2001, 86, 4307-4314]. Furthermore, several studies have shown that levels of glycogen are lower in diabetic patients than in control subjects [Eriksson, J. et al. N. Engl. J. Med. 1989, 331, 337; Schulman, R. G. et al. N. Engl. J. Med. 1990, 332, 223; Thorburn, A. W. et al. J. Clin. Invest 1991, 87, 489], and in addition, genetic studies have shown associations in several populations between type 2 diabetes and mutation in the GYS1 gene encoding the muscle isoform of glycogen synthase [Orhu-Melander, M. et al. Diabetes 1999, 48, 918].
Glycogen synthase is subject to complex regulation, involving phosphorylation at least nine sites [Lawrence, J. C., Jr. and Roach, P. J. Diabetes 1997, 46, 541]. The dephosphorylated form of the enzyme is active. Glycogen synthase is phosphorylated by a number of enzymes of which glycogen synthase kinase 3β (GSK3β) is the best understood [Tadayyon, M. and Smith, S. A. Expert Opin. Investig. Drugs 2003, 12, 307], and glycogen synthase is dephosphorylated by protein phosphatase type I (PP1) and protein phosphatase type 2A (PP2A). In addition, glycogen synthase is regulated by an endogenous ligand, glucose-6-phosphate which allosterically stimulates the activity of glycogen synthase by causing a change in the conformation of the enzyme that renders it more susceptible to dephosphorylation by the protein phosphatases to the active form of the enzyme [Gomis, R. R. et al. J. Biol. Chem. 2002, 277, 23246].
Several mechanisms have been proposed for the effect of insulin in reducing blood glucose levels, each resulting in an increase in the storage of glucose as glycogen. First, glucose uptake is increased through recruitment of the glucose transporter GLUT4 to the plasma membrane [Holman, G. D. and Kasuga, M. Diabetologia 1997, 40, 991]. Second, there is an increase in the concentration of glucose-6-phosphate, the allosteric activator of glycogen synthase [Villar-Palasi, C. and Guinovart, J. J. FASEB J. 1997, 11, 544]. Third, a kinase cascade beginning with the tyrosine kinase activity of the insulin receptor results in the phosphorylation and inactivation of GSK3β, thereby preventing the deactivation of glycogen synthase [Cohen, P. Biochem. Soc. Trans. 1993, 21, 555; Yeaman, S. J. Biochem. Soc. Trans. 2001, 29, 537].
Because a significant decrease in the activity of glycogen synthase has been found in diabetic patients, and because of its key role in glucose utilization, the activation of the enzyme glycogen synthase holds therapeutic promise for the treatment of type 2 diabetes. The only known allosteric activators of the enzyme are glucose-6-phosphate [Leloir, L. F. et al. Arch. Biochem. Biophys. 1959, 81, 508] and glucosamine-6-phosphate [Virkamaki, A. and Yki-Jarvinen, H. Diabetes 1999, 48, 1101].